1. Technical Field
The present invention relates to a liquid analysis device.
2. Background Art
In liquid chromatography devices, ultraviolet (UV)/ultraviolet-visible (UV-VIS) absorbance detectors are most generally used. Particularly, the ultraviolet wavelength band (200 to 380 nm), in which the absorption wavelength bands of various functional groups in organic compounds are present, is being used in various fields. Advantages of the absorbance detector include sensitivity improvement by aligning the measurement wavelength with the wavelength of maximum absorption of substance, and the capability to measure a sample while suppressing the influence of an interfering object by using a measurement wavelength that decreases optical absorption of the interfering component. However, the UV detector cannot detect compounds that do not have absorption in the ultraviolet wavelength band, such as sugars and alcohols.
Research into far-ultraviolet spectroscopy has long been conducted, and it is known that even substances that have hardly any absorption in the ultraviolet region (200 nm or above) have an absorption band in the far-ultraviolet region without fail. However, research has been mostly focused on substances in gaseous phase state, and not much research into liquid state has been conducted. The reason is that, when a spectrum in the far-ultraviolet region is measured, it is necessary to evacuate the inside of the spectroscopic device because of strong absorption by oxygen in the air, making the device complex and expensive. In addition, the absorption spectrum of the solvent used has been so strong that hardly any light was transmitted, making the measurement difficult. Generally, far-ultraviolet light is defined as the light with wavelengths of 10 nm to 200 nm inclusive, while ultraviolet light (also called near-ultraviolet light) is defined as the light with wavelengths of 200 nm to 380 nm.
In recent years, it has become possible to perform far-ultraviolet spectrometry by substituting the air in the spectroscopic device with inert gas such as nitrogen gas. Accordingly, it is now possible to perform absorption spectrum measurement of substance in a solution up to 180 nm using a transmission-type cell with a shortened optical path length of 0.5 mm (Non-Patent Document 1). It is also possible to perform absorption spectrum measurement of liquids up to 120 nm using an attenuated total reflection (ATR) type of spectroscopic device with an extremely shortened effective optical path length of several tens of nm (Non-Patent Document 2).
As a device capable of measuring the reflectance and transmittance spectra of a solid sample in the far-ultraviolet region, a vacuum ultraviolet spectroscopic device is known. The device prevents a decrease in the intensity of incident light on a sample, and has achieved a decrease in measurement time as well as evacuation time by eliminating the need for sample inclination during reflectance measurement, thereby decreasing the size of a sample moving mechanism (Patent Document 1).
FIG. 10 is a schematic diagram of the conventional vacuum ultraviolet spectroscopic device. The light emitted from a light source 901 is passed through a slit 902 and enters a diffraction grating 904. The light of a predetermined wavelength passes through a slit 905, and the intensity of the light transmitted by a sample 909 is detected by a first photodetector 907. The spectroscopic device is provided with an evacuation mechanism 915 for eliminating the influence of optical absorption by oxygen or water vapor. In a typical spectroscope, the optical path is split by a beam splitter and the like installed immediately before the sample, creating reference light and light that is caused to enter the sample for absorbance detection, However, in Patent Document 1, a second photodetector 908 is moved in conjunction with rotation of the diffraction grating 904 using a drive device 910, and light of the same wavelength other than +1 order light is detected as the reference light by the second photodetector 908.
Nevertheless, the above-described devices all have as the primary objective the acquisition of an absorption spectrum, and have not been applied as a detector in liquid chromatography devices due to the issues of detection sensitivity, device size, cost and the like.